The overall goal of this research is to understand the molecular mechanism controlling the function of the avirulence gene product AvrRxv. The hypothesis we will test is that the AvrRxv sequence similarity to mammalian pathogen virulence proteins, YopJ, YopP, AvrA constitutes a functional similarity. This project will focus on testing several predictions based on that hypothesis: mutagenesis of codons for shared domains will eliminate AvrRxv function; random mutagenesis will identify essential amino acids for function; AvrRxv will function when directly expressed by the host cell bypassing the type III secretion system. These studies will facilitate the understanding of how diseases caused by bacterial pathogens can be prevented. Four specific aims are proposed: 1. development of detection system by construction of epitope tagged AvrRxv; 2. site-directed mutagenesis to study functional significance of conserved domains in AvrRxv, AvrBsT, YopJ, YopP, AvrAS and Y4LO; 3. analysis of functional domains by random mutagenesis of avrRxv; 4. analysis of response of host lines to AvrRxv expression in host cells. AvrRxv holds a key position in our understanding of common mechanisms in interactions of bacterial pathogens with their hosts. Knowledge of the functional domains of AvrRxv will provide important information about the other proteins and about virulence effectors in general.